Abstract: Bariatric surgery is effective in treating extreme obesity in adults, and is most commonly used in the 5th decade. As more teenagers develop extreme obesity and seek bariatric surgery, our long term goal is to elucidate the health benefits and risks of surgical weight loss for adolescents. Our central hypothesis is that severe obesity in adolescence is associated with medical and psychosocial impairments which may be more effectively treated with surgery during adolescence rather than later in adulthood. This is based on our observations that adolescents presenting for bariatric surgery 1) have overt and occult medical comorbidities and have already developed psychosocial problems which are likely to worsen, 2) lose significant weight following bariatric surgery, and 3) experience improvement in a number of serious obesity-related conditions such as features of the metabolic syndrome, obstructive sleep apnea, depression, and quality of life. However, compliance by adolescents with prescribed medical regimens can be poor and may adversely affect beneficial outcomes of bariatric surgery performed in adolescence. Thus, the purpose of this proposal is to elucidate for the first time benefits and define complications to be expected when bariatric surgery is performed in adolescence compared to the alternative, bariatric surgery in adulthood. Our Specific Aims are: To determine whether key health indicators significantly differ between adolescents and adults seeking bariatric surgery and determine whether there is an age-related health benefit in performing bariatric surgery earlier rather than later in the lifetime;2) To identify health risks for adolescents and adults undergoing bariatric surgery;3) To document the psychosocial status of adolescents and adults with extreme obesity before and after bariatric surgery. Adolescents will be recruited from several high volume adolescent bariatric centers and a comparison cohort from adult bariatric centers participating in the Longitudinal Assessment of Bariatric Surgery (LABS). By comparison of features of the metabolic syndrome, sleep apnea indices, complications, nutritional status, regimen adherence, and psychosocial status, we will begin to understand medical and psychological health outcomes of bariatric surgery using obesity duration as a moderating variable. This comparison will lead to a better understanding of the plasticity of important medical and psychosocial obesity-related comorbidities in the life-course of those with severe obesity. By also defining risks in the adolescent population, these data will be invaluable for scientifically informing decision-making regarding appropriate timing of surgery for young Americans whose health is increasingly threatened by extreme obesity.